1. Field of the Invention
The present invention relates to an image forming apparatus such as an electric copying machine and, more particularly, to an image forming apparatus having an adjustment mode for various adjustments performed upon unpacking.
2. Description of the Related Art
An electric copying machine, for example, often includes a developing unit for developing an electrostatic latent image on a photosensitive body by a magnetic brush system using a two-component developer material consisting of a toner and a carrier.
In a copying machine using such a developing unit, in order to maintain the image concentration constant, a toner concentration of a developer material contained in the developing unit is detected by a toner concentration sensor. A detection signal from the sensor is compared with a predetermined reference value, and a toner supply means is operated in accordance with the comparison result to supply a toner, thereby always maintaining the toner concentration in the developer material, constant.
A magnetic sensor is sometimes used as the toner concentration sensor. This magnetic sensor detects the toner concentration by detecting a magnetic resistance of the developer material, which changes in accordance with a mixing ratio between a toner and a carrier, and converts a detection signal into an analog voltage signal. The magnetic sensor has a structure in which its output voltage can be varied in accordance with an externally input control voltage.
In a copying machine in which such a magnetic sensor is used as a toner concentration sensor in order to control a toner concentration in a developer material, the toner concentration sensor must be adjusted when the machine is unpacked. That is, when a copying machine is delivered to a user, a serviceman opens its package, performs various initial adjustments, and installs the machine in an operative state. One of the various adjustments performed upon unpacking is an adjustment of a toner concentration sensor. In the toner concentration sensor adjustment, in order to maintain an image concentration constant, an output voltage of the toner concentration sensor is set to be a reference voltage with respect to a reference toner concentration of a developer material.
In order to set the output voltage of the toner concentration sensor to be the reference voltage with respect to the reference toner concentration, a serviceman inputs a control voltage for varying an output signal to the toner concentration sensor, and checks the output voltage from the toner concentration sensor by a digital voltmeter while varying the control voltage by a variable resistor. For this reason, it is difficult to perform an adjustment with high precision, and the adjustment requires a long time. That is, the adjustment operation is very cumbersome.
A copying machine of this type includes a cleaner. After a toner image formed on a photosensitive body by development by a developing unit is transferred onto paper, a rubber blade of the cleaner is brought into contact with the surface of the photosensitive body, thereby scraping off (cleaning) any toner remaining on the surface of the photosensitive body. An adjustment operation of the cleaner is performed as one of the various adjustments performed upon unpacking.
In this cleaner adjustment, the photosensitive body is rotated a predetermined number of times while the blade is in contact with the surface of the drum-like photosensitive body, thereby obtaining a satisfactory contact state of the blade with respect to the surface of the photosensitive body. In this case, since the blade is made of rubber and unused, it is turned up upon rotation of the photosensitive body. In the worst case, the blade may be broken or the surface of the photosensitive body may be damaged.
In order to prevent turn-up of the blade, therefore, a serviceman applies a lubricant called a batting powder to the surface of the photosensitive body, thereby improving slidable contact. For this reason, since the lubricant must be applied to the surface of the photosensitive body, adjustment becomes troublesome and requires a long time. That is, the adjustment operation is very cumbersome.